Control unit for pinhole detectors



Aug. 7, 1951 w. E. COLEMAN CONTROL UNIT FOR PINHOLE DETECTORS Filed June 1, 1949 l2 s J 0 =4 14 IO INVENTOR. WILLIAM E. COLEMAN ATTORNEY Patented Aug. 1, 951

CONTROL UNIT FOR PINHOLE DETECTORS William E. Coleman, Pittsburgh, Pa., assignor to United States Steel New Jersey Company, a corporation of Application June 1, 1949, Serial No. 96,563 6 Claims. (Cl. $-$20) This invention relates to a control unit for pin hole detectors and more particularly to such a device that will detect small holes in thin sheet products such as sheet steel which is used in the manufacture oi tin cans. Conventional pin hole detectors have the disadvantage that they fail to detect the second pin hole when the holes are closely spaced. In some instances the control fails to detect even more than one pin hole when several occur in close succession. Thus some imperfect sheets will pass inspection and be subject to the expense 'of further processing before the defect is discovered.

It is an object of my invention to provide a control unit for a pin hole detector, which unit will operate to detect pin holes regardless of how closely spaced the pin holes may be.

This and other objects will be more apparent after referring to the following specification and attached drawing, in which the single figure is a schematic drawing showing a wiring diagram of the control unit connected to a strip inspecting and shearing line.

Referring more particularly to the drawing the reference numeral 2 indicates an uncoiler for a strip 8. The strip S passes from the uncoiler 2 through side trimming knives 4 and measuring rolls 6 to the shearing drums 8, where the strip is sheared into sheets S of the desired length. The sheared sheets pass over the conveyor III to a deflector l2 which is operated by means of a solenoid l4 to deflect imperfect sheets to a salvage piler IS. The perfect sheets pass over the deflector l2 to a conveyor l8, which delivers the sheets to a prime sheet piler 20. A high intensity light source 22 is located above the strip adjacent the side trimming knives 4 and a bank of light sensitive photoelectric cells 24 is located in a shielded housing under the light sources 22 below the strip. When a section of strip containing a hole passes between the light source 22 and photoelectric cells 24, light passes through the hole and strikes one or more of the photocells. This generates a small voltage impulse which is transmitted to a voltage amplifier 26 where the impulse is amplified to a value of suflicient magnitude to operate the controls of the control unit 28. The pin hole detector may be of the type shown in the patent to Chamberlain et al. No. 2,229,638. The control unit 28 converts the short impulse from the amplifier 26 into an impulse of sufllcient power and duration to operate a solenoid 30 of a strip marker 32 which places a visible mark next to the hole, thus identiiying the section of strip containing the hole.

The control unit also provides an impulse to energize a solenoid in a proportional timer 34 which is driven by a motor 36 which also drives the measuring rolls 6. Thus the timer 34 is in synchronism with the movement oi. the strip. The proportional timer 34 is preferably of the type shown in the patent to Ladrach'No. 2,217,342 and is equipped with a contact mechanism which energizes the solenoid H to tilt the deflector l2 upwardly and direct the sheet containing the pin hole downwardly into the salvage piler It.

The general combination described above is old but has failed to function properly because the control unit does not detect all the holes occurring at close intervals in the strip.

My invention relates particularly to the control unit and provides an overlapping time delay which permits all impulses from the hole detector to be transmitted to the timer 34. The control unit is provided with four grid controlled gas rectifier tubes 38, 40, 42 and 44. Each of these tubes is provided with a grid, plate and cathode. The tubes have indirectly heated cathodes of the conventional type, heaters for which are not shown. These tubes could contain a second or screen grid as well as the control grid shown without changing the operation as described hereinafter. The control grid is able to initiate the flow of current from the plate to the cathode through the tube, but once the current starts to flow the grid no longer is in control. The current can then be stopped only by making the plate potential zero or negative with respect to the cathode. Thus, if the grid is initially sufllciently negative with respect to the cathode, the tube will not conduct, but when the grid voltage is raised in the positive direction even for a very short period of time, the tube will conduct if the plate is positive with respect to the cathode. Conduction will continue until the plate voltage is made zero or negative by external means. A direct current power source 46, such as a battery or rectifier, has its positive side connected to the cathode 38C and its negative side connected to the grid 386 through the resistance 48 so that the grid is normally sufliciently negative to prevent conduction in the tube 38. The amplifier 26 is connected to the grid and cathode so that when a hole occurs in the strip the impulse from the amplifier 26 will make the grid 38G positive with respect to the cathode 38C. The plate 38F is normally connected to a D. C. power source 50 through the normally closed contact 52C of a relay 52 and a relay coil 54. Thus, since its plate is positive with respect to its cathode the tube 38 will eluding said normally open contact and said second relay coil in series, a second normally open contact for the first named relay, a second gridcontrolled gas rectifier tube in circuit with said second normally open contact, means for maintaining the grid of the second tube negative with respect to the cathode, a second normally closed contact, a third relay coil, said last named contact and the third relay coil being connected in series with the plate of the second tube, a normally open contact operated by said third relay coil, a normally closed contact operable by the third relay coil, a D. C. power source, a capacitor connected in parallel with said last named contact to said last named power source, a third rectifier tube, means for maintaining the grid of the third tube negative with respect to the oathode, said capacitor being connected to the grid of the third tube, a fourth relay coil connected in series with the plate of the third tube, said fourth relay coil operating the second normally closed contact, and an A. C. power source connected to the plate of the third tube.

2. A control unit according to claim 1 having a second capacitor, a fourth gas rectifier tube having its grid connected through said second capacitor in circuit with said second normally open contact, the first named capacitor being connected between the plate and cathode of the said fourth tube, and means for maintaining the grid of the fourth tube negative with respect to the cathode.

3. A control unit operable by a voltage impulse comprising agrid controlled gas rectifier tube having a grid, cathode and plate, a direct current power source connected to said grid, means for applying the voltage impulse to said grid, 9. second direct current power source, a normally closed contact, a relay coil, means for connecting the second direct current power source to said cathode and plate through said contact and said relay coil, a normally open contact operated by said relay, a second relay coil for operating the said normally closed contact, a circuit including said normally open contact and said second relay coil in series, a second normally open contact for the first named relay, a second grid controlled gas rectifier tube in circuit with said second normally open contact, a direct current power source having its positive side connected to the cathode of the second tube and its negative side connected to the grid, a resistance in the connection to the last named grid, a second normally closed contact, a third relay coil, said last named contact and the third relay coil being connected in series with the plate of the second tube, a normally open contact operated by said third relay coil, a normally closed contact operable by the third relay coil, a D. 0. power source, a capacitor connected in parallel with said last named contact to said last named power source, a third rectifier tube, a direct current power source having its positive side connected to the cathode of the third tube and its negative side connected to the grid, a resistance in the connection to the last namedgrid, said capacitor being connected to the grid of the third tube, a fourth relay coil connected in series with the plate of the third tube, said fourth relay coil operating the second normally closed contact, and an A. C. power source connected to the plate of the third tube.

4. A control unit operable by a voltage impulse comprising a grid controlled gas rectifier tube having a grid, cathode and plate, a direct current power source connected to said grid, a second direct current power source, a normally closed contact, a relay coil, means for connecting the second direct current power source to said cathode and plate through said contact and said relay coil, a normally open contact operated by said relay, a second relay coil for operating the said normally closed contact, a circuit including said normally open contact and said second relay coil in series, a second normally open contact for the first named relay, a second grid controlled gas rectifier tube in circuit with said second normally open contact, a direct current power source having its positive side connected to the cathode of the second tube and its negative side connected to the grid, a resistance in the connection to the last named grid. a second normally closed contact, a third relay coil, said last named contact and the third relay coil being connected in series with the plate of the second tube, a normally open contact operated by said third relay coil, a normally closed contact operable by the third relay coil, a D. C. power source, a capacitor connected in parallel with said last named contact to said last named power source, a third rectifier tube, a direct current power source having its positive side connected to the cathode of the third tube and its negative side connected to the grid, a resistance in the connection to the last named grid, said capacitor being connected to the grid of the third tube, a fourth relay coil connected in series with the plate of the third tube, said fourth relay coil operating the second normally closed contact, an A. C. power source connected to the plate of the third tube, a second capacitor, a fourth gas rectifier tube having its grid connected through said second capacitor in circuit with said second normally open contact, the first named capacitor being connected between the plate and cathode of the said fourth tube, a direct current power source having its positive side connected to the cathode of the fourth tube and its negative side connected to the grid, and a resistance in the connection to the last named grid.

5. A control unit operable by a voltage impulse comprising a grid controlled gas rectifier tube having a grid, cathode and plate. means for maintaining the grid negative with respect to the cathode, means for app s the Voltage im ulse to said grid, a power source, a normally closed contact. a relay coil, means for connecting the power source to said cathode and plate through said contact and said relay cell, a normally open contact operated by said relay, a second relay coil for operating the said normally closed contact, a circuit including said normally open contact and said second relay coil in series, a second normally open contact for the first named relay, a second tube in circuit with said second normally open contact, means for maintaining the grid of the second tube negative with respect to the oathode, a second normally closed contact, a third relay coil, said last named contact and the third relay coil being connected in series with the plate of the second tube, a normally open contact operated by said third relay coil, a normally closed contact operable by the third relay coil, a power source, a capacitor connected in parallel with said last named contact to said last named power source, a third tube. means for maintaining the grid of the third tube negative with respect to the cathode, said capacitor being connected to the grid of the third tube, a fourth relay coil connected in series with the plate of the third tube, said fourth relay coil operating the second normaily closed contact, and a power source connected to the plate of the third tube.

6. A control unit according to claim 5 having a second capacitor, a fourth tube having its grid connected through said second capacitor in circuit with said second normally open contact,the first named capacitor being connected between the plate and cathode of the said fourth tube, and means for maintaining the grid of the fourth tube negative with respect to the cathode.

- WILLIAM E. COLEMAN.

acreamqccs crran The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Firestone Dec. 2, 1930 Swart Oct. 16, 1934 Ladrach Oct. 8, 1940 Chamberlin Jan. 28, 1941 Viebahn June 24, 1941 

